It is well known to terminate a conductor with an impedance which is ideally matched to the dynamic impedance of the conductor in order to reduce signal reflections and concomitant degradation of data transmitted on the conductor. One such terminator comprises a resistor having a resistance value nominally matched to that of the conductor. While the nominal resistance value may match a typical conductor impedance, tolerances can affect the conductor and resistor impedances, thereby degrading the resulting impedance "match". Moreover, the resistance value of such a terminator is fixed so that its use to terminate conductors having different dynamic impedances is precluded.
Another type of terminator utilizes an active device and thus, may be referred to as an active terminator. An example of an active terminator is one utilizing a field effect transistor (FET) biased to saturation. In this operating condition, the FET has a highly non-linear, current source characteristic which generally does not reduce signal reflections as well as terminators having a linear, substantially resistive characteristic.
As is known in the field of bus terminators, only the ends of a communications bus should be terminated with an impedance matched to the impedance of the bus. Bus termination at intermediate points, or nodes along the bus can disadvantageously effect signal integrity. As is also known, the impedance of the bus sought to be matched by a terminator varies in accordance with the length of the bus.